When starting seeds for gardening, the first thing to do is to read the back of the seed packet for instructions. Most seed packets inform the gardener to plant the seed or seedling in loamy, well-drained soil with rich organic matter.
Plants, like people, want their conditions to be perfect – plenty of sun, not too hot, and not too cold, good soil/food and enough to drink. If given perfect conditions plants and people thrive, but perfect conditions are not always available. And sometimes we just need to play the hand we’re dealt.
In this article, we will discuss the importance of soil health and the underground conditions that can make or break the long-term health of our trees.
Soil vs. Dirt
Soil is sometimes referred to as dirt. When discussing a plant’s relationship with the ground it is planted in, soil is often the term that arborists or landscapers use. Using the word soil alludes to the living medium that exists in the underground world. In contrast, the word dirt conjures up images of kids playing with toy trucks on a pile of lifeless earth.
Understanding the complexity of soil can help explain a tree’s ability to thrive in certain environments, or struggle to live in others.
Compacting the Health Out of Your Soil
A common theme that tends to find its way into discussions about trees is soil health and compaction. Urban soils are often intentionally compacted to support roads and sidewalks. Heavy aggregates are added and compacted into the ground before foundations are laid. Engineers prioritize compacted, level beds to avoid future shifting and settling in our urban infrastructure.
A typical new development is often excavated and graded within an inch of its life. Any semblance of soil health is scraped away to achieve a well graded and pitched landscape to move water away from homes and business quickly. After the last piece of heavy equipment has finished squishing the last bit of air out of the soil, a thin layer of soil, or in this case dirt, is spread across into a parking lot smooth surface and topped with dusting of grass seed.
Most urban zoning codes require this newly built development to include a certain number of trees and shrubs to go along with the fresh carpet of grass. Unfortunately, for the new trees and shrubs their new home to be is a bleak future with long odds for survival.
Soil Is a Living Medium
Soil is a living ecosystem. And soil health is predicated on the ability of natural systems to very slowly, sometimes over thousands of years, add layers of decomposing plants, animals and minerals in a rich bed of life. An undisturbed forest floor is a sea filled with bacteria, fungi and insects that help keep the trees thriving. Tree needs are easily met in rich soil conditions that have evolved over time.
Trees growing in urban soils often face a different set of circumstances. Underground conditions to promote proper root growth are ideally like the conditions on the seed packet- loamy, well-drained soil with rich organic matter. If the tree is lucky, it may get one of the above.
Pore Space for Soil Health
Pore space is also critical for healthy tree roots. Pore space provides room for root growth, air for respiration and nooks and crannies that water can move through. Soils with large aggregates, some sand or bonded clay particles, provide ideal growing conditions that contain abundant pore space. Soils with large aggregates tend to feel more loose and crumbly.
Tree roots need the oxygen in pore space to be able to grow. Roots perform respiration by utilizing oxygen in the soil and sugars produced in the leaves to produce energy. Energy produced from respiration can be used to elongate root growth in the tips of the fine feeder roots, or increase the diameter of structural roots closer to the trunk. New root growth will take advantage of pore space to continually expand and search for more nutrients and water in the soil.
The amount and depth of oxygen in soil can determine the depth of the tree’s root system. Since most of the oxygen and organic matter are near the surface of the soil, most of the tree’s root system will be located closer to the surface of the soil as well.
Compacted soils that are layered over a hardpan of heavy clay or rock easily become saturated and devoid of oxygen. Poorly drained soils will limit the amount of oxygen and result in poor root growth and soil health.
Photo by Tim Hüfner on Unsplash
Ways to Improve Soil Health
If your soil has been compacted through construction or vehicles, or you suspect you have poor soil health for some reason, there are several actions you can take.
Air spading uses compressed air to loosen up the compacted soil in the tree’s root zone.
Soil can be amended with compost or biochar to improve fertility and pore space. This added fertility can benefit microorganisms in the soil and provide nutrients to the fine feeder roots.
The easiest step in improving soil health is to allow mother nature to take the lead. In a forest setting, organic matter is allowed to accumulate on the forest floor in the form of fallen leaves and twigs. The decomposition of leaves beneath the tree’s canopy adds nutrients to the soil, feeds the beneficial fungi, bacteria and microorganisms and helps insulate and protect the soil from temperature fluctuation.
In most backyard settings, the balance between a healthy lawn and promoting healthy soils for tree growth can require some compromises to be made. Having room for kids and games, while also protecting the root zone around high value shade trees can both be accomplished.
Placing a ring of mulch around your trees can protect the root zone from compaction, spare the trunk from damage from string trimmers or mower decks, and add organic matter with the decomposition and replenishment of mulch. Mulching is one of the easiest, cheapest and most effective ways to improve soil health.
Whether you are establishing new trees or caring for older ones, protecting and improving the health of the soil around them will pay dividends in the form of long-term health and increased growth rates.
Having a good sense of whether your soil is compacted and in need of aeration, or lacking organic matter will help you understand the needs of your young and old trees.
Not sure what your trees need? Schedule an appointment and we’ll make a visit to assess the health of your trees and soil.